Scientists from Yale University and the Albert Einstein College of Medicine have produced a study that finds patients with type O blood were at double the risk of diminished ovarian (egg) reserve than women of other blood types.

They’re presenting their results to the American Society for Reproductive Medicine (ASRM) annual conference in Denver.

However, one expert on fertility says more research needs to be done after these “surprising and stark” findings.

Type O Blood and Fertility

Researchers measured women under age 45 for levels of the reproductive hormone FSH. Women with an FSH level greater than 10 are considered to have diminished ovarian reserve.

They made adjustments for other fertility factors including age and BMI (body mass index), then compared women’s blood types and FSH levels.

Women with types A or AB blood were significantly less likely to have an FSH greater than 10 than were women with types O or B blood.

“This is a novel look at a poorly understand part of reproductive aging. Through studies like these we will be better able to understand the complexities of the human reproductive system,” says William Gibbons, MD, president of the ASRM.

In the U.S., 45% of the population is type O, 40% type A, 11% type B, and 4% type AB.

More Research Needed

Richard Fleming, PhD, is the scientific director of the Glasgow Centre for Reproductive Medicine. “The results do seem quite surprising and stark in the distribution that you see between the blood groups,” he tells WebMD.

However, he cautions that the FSH method isn’t the most accurate for measuring fertility. “It is fairly good at assessing extremes of egg reserve, but it can’t differentiate between normal and high and perhaps not even low-normal.”

He says a better test is to get a woman’s anti-mullerian hormones (AMH) measured. “It is a more precise marker of ovarian reserve,” he says.

Should women with type O blood wanting to have a baby worry? “It is an interesting, and to me, quite surprising finding that needs to be substantiated. Therefore, the implication for someone with type O is number one, don’t worry.”

“Number two,” if women have fertility concerns, Fleming says, “get their AMH measured, not their FSH.”